One of the world’s most beloved beverages comes from a species of plant found in the fourth largest family of flowering plants. Rubiaceae, also known as the coffee or bedstraw family, consists of around 13,500 species, placing it behind just Asteraceae, Orchidaceae, and Fabaceae for the most number of species. Coffea arabica, and other species in the genus Coffea, are grown for their fruits which are used to make coffee. This makes Rubiaceae one of the most economically important plant families. A family this size is bound to be home to a weed or two, and in fact, one of the most widespread and obnoxious weeds is also a member of Rubiaceae.
Galium aparine, known commonly by a slew of names including cleavers, occurs naturally across large portions of Europe, Asia, North Africa, and possibly even parts of North America. It has been introduced as a weed in many locations across North America, South America, Australia, New Zealand, Japan, and parts of Africa. It is of particular concern in agricultural settings where its lengthy, sprawling branches and sticky leaves get tangled up in harvesting equipment, while its tiny, prickly fruits get mixed in with seeds of similar size like canola.
Sticky willy, as it is also known, is an annual plant that, in some cases, can have two generations per year – one in the spring (having germinated the previous fall) and one in the summer. Its stems are square, though not as sharply square as plants in the mint family, and can grow to around six feet long. They are weak, brittle, and don’t stand upright on their own; instead they are found scrambling across the ground or, when given the opportunity, climbing up the lengths of other plants in order to reach the sunlight. Leaves occur in whorls of six to eight and are simple and slender with entire margins. Flowers are produced at leaf axils along the lengths of the branches and are tiny, four-petaled, star-shaped, and greenish white. Fruits are borne in pairs and are round, single-seeded, indehiscent nutlets. The stems, leaves, and fruits are covered in stiff, hooked hairs or trichomes, earning it other names like catchweed bedstraw, grip grass, stickyweed, and velcro plant.
Galium aparine is a climbing plant, but unlike other climbing plants, it doesn’t twine up things or produce structures like tendrils to hold itself up. Instead, its ability to climb is made possible by its abundant bristly hairs. A paper published in Proceedings of the Royal Society B (2011) investigates the way G. aparine climbs up other plants using the hairs on its leaves. A close inspection of the leaves reveals that the trichomes on the top of the leaf (the adaxial leaf surface) differ significantly from those found on the bottom of the leaf (the abaxial leaf surface). Adaxial trichomes curve towards the tip of the leaf, are hardened mainly at the tip, and are evenly distributed across the leaf surface. Abaxial trichomes curve towards the leaf base, are hardened throughout, and are found only on the midrib and leaf margins.
Having different types of hairs on their upper and lower leaf surfaces gives cleavers an advantage when it comes to climbing up neighboring plants. The authors of the paper describe the technique as a “ratchet mechanism.” When the upper surface of their leaf makes contact with the lower surface of another plant’s leaf, the flexible, outwardly hooked trichomes inhibit it from slipping further below the leaf and allow it to easily slide out from underneath it. When the lower surface of their leaf makes contact with the upper surface of another plant’s leaf, the stiff, inwardly hooked trichomes keep it attached to the leaf even if the other leaf starts to slip away and allows it to advance further across the leaf for better attachment and coverage. Using this ratchet mechanism, cleavers climb up the leaves of other plants, keeping their leaves above the other plant’s leaves, which gives them better access to sunlight. The basal stems of cleavers are highly flexible, which keeps them from breaking as the plant sways in the wind, tightly attached to their “host” plant.
The hooked trichomes on the tiny fruits of cleavers readily attach to the fur and clothing of passing animals. The nutlets easily break free from the plants and can be transported long distances. They can also be harvested and made into a lightly caffeinated tea. Harvesting the fruit takes time and patience. I spent at least 20 minutes trying to harvest enough fruits for one small cup of cleavers coffee. The fruits don’t ripen evenly, and while I tried to pick mostly ripe fruits, I ended up with a selection of fruits in various stages of ripeness.
To make cleavers coffee, first toast the seeds for a few minutes in a pan heated to medium high, stirring them frequently. Next, grind them with a mortar and pestle and place the grinds in a strainer. Proceed as you would if you were making tea from loose leaf tea.
The toasted fruits and resulting tea should smell similar to coffee. The smell must not be strong, because my poor sense of smell didn’t really pick up on it. The taste is coffee-like, but I thought it was more similar to black tea. Sierra tried it and called it “a tea version of coffee.” If the fruits were easier to collect, I could see myself making this more often, but who has the time?
The leaves and stems of Galium aparine are also edible, and the plant is said to be a particular favorite of geese and chickens, bringing about yet another common name, goosegrass. In the book Weeds, Gareth Richards discusses the plant’s edibility: “It’s edible for humans but not that pleasant to eat; most culinary and medicinal uses center around infusing the plant in liquids.” Cooking with the leaves or turning them into some sort of spring tonic is something I’ll consider for a future post about eating cleavers.
awkward botany 